1. Field of the Invention
The present invention relates to an electronic apparatus comprising at least a display portion and a quartz crystal oscillator.
2. Background Information
There are many electronic apparatuses comprising at least a display portion and a quartz crystal oscillator. For example, cellular phones, wristwatches and pagers comprising a quartz crystal oscillator are well known. Recently, because of high stability for frequency, miniaturization and the light weight nature of these electronic apparatus, the need for an electronic apparatus comprising a smaller quartz crystal oscillator with a high frequency stability has arisen. For example, the quartz crystal oscillator with a quartz crystal tuning fork resonator, which is capable of vibrating in a flexural mode, is widely used as a time standard in an electronic apparatus such as cellular phones, wristwatches and pagers. Similar to this, the same need has also arisen for an electronic apparatus comprising a width-extensional mode quartz crystal resonator and a thickness shear mode quartz crystal resonator.
Heretofore, however, it has been impossible to obtain an electronic apparatus comprising a smaller quartz crystal oscillator with a conventional miniaturized quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance and a high quality factor. When miniaturized, the conventional quartz crystal tuning fork resonator capable of vibrating in a flexural mode, as shown in FIG. 10 (which has electrodes on the obverse faces 203, 207, reverse faces 204, 208 and the four sides 205, 206, 209, 210 of each tuning fork tine, as also shown in FIG. 11—a cross-sectional view of tuning fork tines of FIG. 10), it has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field (i.e. Ex becomes small), as a result of which the resonator has a low frequency stability, a large series resistance and a reduced quality factor. In FIG. 10, a conventional tuning fork resonator 200 is shown with tuning fork tines 201, 202 and a tuning fork base 230.
Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992A and International Patent No. WO 00/44092 were published and teach grooves and electrodes constructed at tuning fork tines of a flexural mode, tuning fork, quartz crystal resonator. However, they teach nothing about a quartz crystal oscillator of the present invention having novel shape, novel electrode construction and figure of merit M for a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and about a relationship of an amplification circuit and a feedback circuit which construct a quartz crystal oscillating circuit.
Additionally, for example, there has been a big problem in the conventional quartz crystal oscillator with the conventional quartz crystal tuning fork resonator, such that a fundamental mode vibration of the resonator jumps to a second overtone mode vibration by shock or vibration.
In addition, as a quartz crystal resonator of the prior art, a NS-GT cut coupling quartz crystal resonator which vibrates in the coupled width-extensional mode and length-extensional mode is well known. FIG. 12a and FIG. 12b show a top view and a side view of the conventional NS-GT cut coupling quartz crystal resonator. In FIG. 12a and FIG. 12b, the resonator 300 comprises a vibrational portion 301, connecting portions 303, 306 and supporting portions 304, 307. The supporting portions 304 and 307 include respective mounting portions 305 and 308.
Likewise, as shown in FIG. 12a and FIG. 12b, electrodes 302 and 311 are disposed on the upper and lower faces of the vibrational portion 301, the electrode 302 extends to the mounting portion 305 through the connecting portion 303, while the electrode 311 extends to the mounting portion 308 through the connecting portion 306. The electrodes 302 and 311 have opposite electrical polarities, and two electrode terminals are constructed.
Now, when an alternating current(AC) voltage is applied between the electrodes 302 and 311, an electric field Et occurs alternately in the thickness T direction, as shown by arrow signs of the solid and broken lines in FIG. 12b. As a result, the coupled width-extensional mode and the length-extensional mode whose frequencies are inversely proportional to width W and length L of the vibrational portion, respectively, can be excited at the same time, and the NS-GT cut coupling resonator coupled in inverse phase is provided. The above-mentioned resonator is formed integrally by a chemical etching process.
Furthermore, the lager the area of vibrational portion for the NS-GT cut resonator becomes (low frequency), the smaller series resistance R1 becomes and the larger a quality factor Q becomes. Also, the NS-GT cut resonator with excellent frequency temperature behavior is determined by a dimensional ratio W/L, and which has a value of 0.95 approximately. In order to get a frequency higher than 4 MHz, it is necessary to decrease the area of the vibrational portion for the resonator.
According to the miniaturization and the light weight nature of an electronic apparatus comprising a quartz crystal oscillator with an output signal of a frequency higher than 4 MHz, a miniature quartz crystal oscillator comprising a NS-GT cut resonator with the higher frequency is also required with a small series resistance R1 and high quality factor Q.
It has been, however, impossible to provide an electronic apparatus comprising a miniature quartz crystal oscillator having a NS-GT cut resonator with a frequency higher than about 4 MHz with a small series resistance R1 and a high quality factor Q because the area of vibrational portion for the resonator becomes very small to get the higher frequency, and more an electromechanical transformation efficiency becomes very small, so that a series resistance R1 becomes large and a quality factor Q also becomes small.
It is, therefore, a general object of the present invention to provide embodiments of an electronic apparatus and a quartz crystal oscillator, which constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability, a small series resistance and a high quality factor, or embodiments of a quartz crystal oscillator, which also constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a width-extensional mode quartz crystal resonator having a frequency higher than 4 MHz, a small series resistance and a high quality factor, which overcome or at least mitigate one or more of the above problems.